Download gene sequence

Outline
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Introduction to Gene Expression
Transcription and Types of RNA
The Genetic Code
Translation
Gene Expression
Flow of Genetic Information
• A gene is a sequence
of DNA that codes for
a sequence of amino
acids in a specific
protein.
• Genetic information
flows from DNA to
RNA in order to direct
protein synthesis.
• Protein synthesis is a
two step process.
DNA Gene
Sequence
Transcription
RNA
Transcript
Translation
Amino
Acid
Sequence
Transcription - Overview
• Occurs in the nucleus.
• A replication fork opens up
at a specific gene
sequence of DNA.
• RNA polymerase attaches
and adds RNA nucleotides
in the 5’ – 3’ direction.
• RNA transcript leaves the
nucleus and enters the
cytoplasm – where
translation occurs.
Gene Sequence in DNA
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A specific region of DNA
Consists of three parts:
1. Promoter – RNA attaches
2. Operator – actual gene sequence
3. Termination Signal – “end” of the gene
PROMOTER
OPERATOR
TERMINATION
SIGNAL
Transcription - Steps
1. Initiation
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DNA unwinds at the gene sequence
RNA pol binds to the promoter region
2. Elongation
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RNA pol “reads” the template strand
RNA adds RNA nucleotides and the RNA strand
grows
3. Termination
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RNA pol reaches the termination sequence
RNA strand detaches from the DNA(Rho protein)
RNA pol detaches from the DNA
Types of RNA
• Three types of RNA are
produced and they each
play a specific role in
protein synthesis.
mRNA
RNA
tRNA
rRNA
mRNA – Messenger RNA
• Single stranded polymer
that carries the code for
protein synthesis.
• The gene is stored in the
library of DNA and
mRNA is the “workable”
code that enters the
cytoplasm.
tRNA – Transfer RNA
• Small chain of RNA that
transfers amino acids to
the growing protein chain
at the ribosome.
• The tRNA matches up to
the mRNA code with its
anti-codon loop.
• Many types of tRNA
molecules.
rRNA – Ribosomal RNA
• A component of ribosomes – the site of protein synthesis
in the cytoplasm.
• Ribosomes are made of rRNA and proteins, arranged
into two sub-units.
Translation - Overview
• The process of protein synthesis – occurs
in the cytoplasm of the cell, specifically at
the ribosomes.
• 3 nucleotides of mRNA are “read” at a
time and tRNA brings the correct amino
acid to the ribosome.
• The amino acid is attached to the growing
protein chain in the ribosome.
The Genetic Code
• The genetic code uses three bases of
nucleotides to represent one amino acid.
• 3 nucleotide bases = 1 codon
• There are 64 possible codons and only 20
natural amino acids.
Why???
Translation - Steps
1. Initiation
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Ribosome assembles around the mRNA – AUG codon
tRNA for methionine attaches to the ribosome.
2. Elongation
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Ribosome moves along the mRNA strand
tRNA brings amino acid to one site of ribosome –
codon/anti-codon interaction
Amino acids get connected at the second site
Process continues until stop codon is reached.
3. Termination
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Polypeptide detaches
Ribosome detaches, mRNA breaks down
Codon/Anti-Codon Interaction